1. Field of the Invention
The present invention relates generally to improvements in a printing apparatus having a carriage which carries a print-erase head, a print ribbon and an erase ribbon and which is moved along a platen. More particularly, the invention is concerned with improvements to minimize the size and weight of the mechanisms supported on the carriage.
2. Discussion of the Related Art
Some of the known printers such a typewriters are equipped with a carriage which is reciprocable in a longitudinal direction of a platen. The carriage is adapted to support a mechanism to feed a print ribbon, a mechanism to feed an erase or correction ribbon, a print/erase head, and other devices, and is reciprocated by a drive source such as an electric motor. The ribbon feed mechanisms are required to be activated at suitable times. It is desirable to shift the active portion of the print ribbon between a rest or inoperative position, and a printing or operative position between the platen and the print/erase head. However, this shifting of the print ribbon is not essential. On the other hand, it is essential that the active portion of the erase ribbon be shifted between its rest and erasing positions. In the case where the print ribbon is not adapted to be elevated and lowered between its printing and rest positions, a character printed on the recording medium is erased while the active portion of the erase ribbon is located between the print ribbon and the platen (recording medium). More specifically, the print/erase head is activated to impact the appropriate type font against the recording medium via the print and erase ribbons, so that the character is erased by the impacted area of the erase ribbon. In the case where the print ribbon is adapted to be shifted between its printing and rest positions, the erasure of a character is effected with the print ribbon moved to its rest position and with the erase ribbon moved to its erasing position. In this case, the print/erase head is activated to impact the appropriate type font against the recording medium via the erase ribbon only.
As is apparent from the foregoing description, it is required that the print ribbon feed mechanism, the erase ribbon feed mechanism, the erase ribbon lift mechanism, and other devices, be operated while they are supported on the carriage. If the above three mechanisms associated with the print and erase ribbons are operated by three exclusive drive devices, the corresponding three separate or independent drive sources are necessary. The mounting of these three drive sources on the carriage will not only increase the cost of the printer, but also increase the mass of an assembly of the carriage and the devices mounted on the carriage, thereby making it difficult to feed the carriage assembly at a high rate for increased printing efficiency.
A known solution to the above drawback utilized reciprocating movements of the carriage by the carriage drive motor, for feeding the print ribbon, for example. In this instance, a shaft is rotatably supported on the carriage so that the shaft is rotated by means of its movement relative to the printer frame when the carriage is reciprocated. The rotating movement of the shaft is transmitted to the print ribbon feed mechanism, to feed the print ribbon. Generally, this arrangement uses a one-way clutch which permits transmission of the rotation of the shaft in one of opposite directions to the print ribbon feed mechanism, but inhibits transmission of the shaft rotation in the other direction.
Although it is considered possible to utilize the carriage drive source to feed the erase ribbon and shift its active portion in the same manner as mentioned above, there have been no attempts to utilize the carriage drive source for feeding both of the print and erase ribbons, and/or for feeding the print ribbon and shifting the erase ribbons. While the printer is in a normal printing mode, the feeding of the print ribbon is required, but the feeding and shifting of the erase ribbon are unnecessary. In a correction mode for erasure or correction of characters, on the contrary, the feeding of the print ribbon is not required while the feeding and shifting of the erase ribbon are necessary. Thus, the print ribbon feed mechanism, and the erase ribbon feed or shifting mechanism require a drive force at different times. For this reason, it has been considered difficult to obtain a particularly satisfactory arrangement in which the above two mechanisms are operated by the carriage drive source.